In medical practice it is frequently necessary to assist the breathing of a patient. Most frequently this is done by intubating the patient and applying periodic positive air pressure through the intubation into the patient's lungs. Intubation is associated with a number of clinical and practical disadvantages.
The alternative to intubation is to use some form of external ventilator apparatus. External ventilator apparatus of the so-called "Cuirass Ventilator" type has a long history. Until recently, such devices have been of limited usefulness. In our British Patent Specification No. 2226959A, we have described chest enclosures for use in producing assisted ventilation which have proved successful in practice. However, we have found that there are a number of aspects in which still further improvement is possible.
First, we have found that there is some tendency for the top surface of the chest enclosure or shell to move downwardly when suction is applied to the enclosure by the oscillator so as to produce a substantial sub-ambient pressure within the enclosure formed by the shell. The top surface of the shell is drawn downwardly against the patient's chest creating pressure on the chest partially blocking its expansion and this reduces the effectiveness of the ventilating action of the air oscillator to a degree.
Secondly, one of the principal advantages of the chest enclosure described in the application referred to above is the speed with which it can be applied to a patient. The chest enclosure described had bands of closed-cell foam extending from its side edges which were to be wrapped around the patient in overlapping relationship and fastened by straps. We have found that it is possible to devise an edge seal for the shell which enables the shell to be applied over a patient and to form a seal sufficient for use whilst the patient is lying supine and still, even without the use of fastening straps, at least as a temporary measure.
Furthermore, we have devised a form of seal for the shell still better adapted to resist the escape of super-ambient pressure from the shell during use.